This application claims the priority benefit of Japanese application serial no. 2001-081267, filed on Mar. 21, 2001 and 2001-187577, filed on Jun. 21, 2001.
1. Field of the Invention
This invention relates in general to an optical path element, an optical switching element, a spatial light modulator and an image display apparatus. More specifically, the invention relates to an optical path element, an optical switching element and a spatial light modulator, and an image display apparatus using the above, by which simpler structure, superior durability, low device cost, and high utilization rate for light can be achieved.
2. Description of Related Art
An optical switching device is used for switching the light by changing the reflection direction of an incident light. For example, Japanese Laid Open H05-196880 discloses an optical switching device and a spatial light modulator using the optical switching device, in which a plurality of tiny rotational mirrors are arranged in a two dimensional array.
FIG. 19 shows a plane view of a conventional spatial light modulator disclosed in Japanese Laid Open H05-196880. As shown, only a torsion beam reflection surface 11 and a beam supporting post 12 are observed. FIGS. 20A and 20B show a cross-sectional view of one of rotational mirrors of the spatial light modulator in FIG. 19. FIG. 20A is a cross-sectional view along a hinge and FIG. 20B is a cross-sectional view perpendicular to FIG. 20A. The beam 11 can be rotated around a ground electrode 14 by the beam supporting post 12 due to the twist of the hinge 13 connected to the post 15. The driving force is given by applying a voltage to an address electrode 17 supported by the post 16. The voltage applied to the address electrode 17 is by transmitting a signal through a metal layer 18, in which the signal is from a CMOS circuit (not shown) formed on a substrate 19. The rotational status of the beam 11 varies for each rotational mirror so that the incident light can be spatially modulated in a two-dimensional manner.
According to the above structure, in order to obtain a large rotational angle, the structure of the rotational mirror becomes very complicated and the manufacturing cost increases.
Japanese Laid Open H11-202222 discloses another exemplary optical switching device, the operation of which is explained in FIG. 21. The optical switching device comprises a light transmission part 21 provided with a full reflecting plane 22 for fully reflecting light and transmitting it, a prism 31 capable of capturing, reflecting and emitting evanescent light while an extracting plane 32 is near the full reflecting plane 22, and a driving part 40 for driving the prism 31, which are all laminated in this order in the light emitting direction. The cell at the right side shown in FIG. 21 activates the driving part 40 such that the prism 31 moves to a position above the extraction distance where the evanescent light would leak. At this time, as shown in FIG. 21, the light 1 transporting in the light transmitting element 21 is totally reflected at the total reflection surface 22 and then the reflected light 2 emits rightwards. When the driving part is deactivated, as in the cell at the left side shown in FIG. 21, because the prism 31 is near to a position under the extraction distance where the evanescent light would leak, the light I transporting in the light transmitting element 21 is not reflected at the total reflection surface 22 but enters the prism 31. The light that enters the prism 31 is then reflected at the reflection surface 31a of the prism 31 and then passes through the light transmitting element 21 to emit as the light 3 shown in FIG. 21.
According to the above method, the extracted and the unextracted states of the evanescent light can be switched. This structure is suitable for a tiny displacement about the wavelength of the light, and a simple driving mechanism can be used. However, because the mechanism of the prism 31 in FIG. 21 is a very complicated structure, it is very difficult to form a plurality of tiny-size prisms on the substrate uniformly, causing problems such as low yield rate and high cost etc. Additionally, as the prism 31 approaches the total reflection surface 22 of the light transmitting element 21, the Van der Walls force or the liquid bridging force occurs between them, and therefore it is very hard to separate the prism 31 from the total reflection surface 22.
Japanese Laid Open 2000-171813 discloses another exemplary optical switching device, which is shown in FIG. 22. A light transmitting element for transmitting light by the total reflection is provided such that the alignment of a liquid crystal can be controlled by applying a voltage to the liquid crystal 60 that is in contact with the light transmitting element 50. Therefore, the effective index of refraction can be varied with respect to an ordinary light and an extraordinary light. The switching mechanism can be made between the first state, where the incident light (linear polarized) 1 is emitted as a total reflection light 2, and the second state, where the penetrated light of the incident light is reflected by a reflection film 61 to change its direction and then is emitted as a reflection light 3. In FIG. 22, the light switching device further comprises a transparent electrode 51, a driving IC for the liquid crystal 70 and electrode terminals 71.
As described above, because there are no mechanical driving parts, the foregoing problems do not happen. However, because of the total reflection at the interface of the light transmitting element and the liquid crystal, it needs a material with a high index of refraction to make the light transmitting element, or a large incident angle is required, thereby the material cost becomes very high and the optical system is very complicated. Accordingly, it is not suitable for application in practice, because, for example, the light utilization rate is lowered.
To solve the aforementioned problems, the invention provides an optical path element, an optical switching element and a spatial light modulator, and an image display apparatus using the above, by which simpler structure, superior durability, low device cost, and high utilization rate for light can be achieved.
Therefore, it is an object of the invention to provide an optical switching element, which can be easily made at low cost.
It is another object of the invention to provide an optical switching element, which has a high S/N ratio and a small driving energy.
It is still another object of the invention to provide an optical switching element, which has a fast response time and a low light loss.
It is still another object of the invention to provide a spatial light modulator, of which the structure can be simplified, the durability is high, the cost can be reduced, and the light utilization rate can be increased.
It is still another object of the invention to provide a low-cost image display apparatus.
According to the foregoing description, an object of this invention is to provide an optical switching element, comprising: a first light transmitting element, having a first light incident surface, a second light incident surface that is not parallel to the first light incident surface, and a light outgoing surface; a reflection substrate, arranged opposite to the second light incident surface of the first light transmitting element and having a first reflection surface with a predetermined angle that is not parallel to the second light incident surface, wherein a reflected light passes through the first light transmitting element and the reflection substrate and then is reflected by the first reflection surface of the reflection substrate; and an index variable material, sandwiching between the first light transmitting element and the reflection substrate, which has an index of refraction that is variable according to an applied external signal. By varying the index of refraction of the index variable material, an angle formed by the reflected light and a normal line of the light outgoing surface is changed such that an emitting direction of the reflected light is changed.
Preferably, the second light incident surface and the light outgoing surface of the first light transmitting element are not in parallel.
The optical switching element is switched between a first state and a second state, wherein the first state satisfies sin xcfx861xe2x89xa7na/n1, and the second state satisfies sin xcfx861 less than na/n1, in which n1 is the index of refraction of the first light transmitting element, na is an index of refraction of a material surrounding the first light transmitting element, and xcfx861 is the angle formed by the reflected light and a normal line of the light outgoing surface.
The optical switching element further comprises a second light transmitting element that at least has a light incident surface that is substantially parallel and opposite to the light outgoing surface of the first light transmitting element within a predetermined distance; and a light outgoing surface that is not parallel to the light incident surface of the second light transmitting element.
In addition, the optical switching element further comprises a light transmitting plate that is optically in contact with the second light incident surface of the first light transmitting element and has an index of refraction substantially the same as that of the first light transmitting element.
The reflection substrate further comprises a second reflection surface having a tilt angle less than 90xc2x0xe2x88x92xcex82max tilted from the reflection substrate and a common edge shared with the first tilt surface, wherein the angle xcex82max is defined as a maximum of an angle formed between a normal line of the second light incident surface and an incident light that enters the index variable material from the second light incident surface of the first light transmitting element.
The optical switching element can further comprise a plurality of reflection surfaces that are formed on the reflection substrate, wherein the reflection surfaces correspond respectively to driving elements used for applying external signals to the index variable material.
The index variable material mentioned above can comprise a liquid crystal or a compound of a polymer and a liquid crystal, where the liquid crystal is dispersed in a polymer matrix. The liquid crystal is a droplet having a grain size below one-fifth wavelength of the incident light. All liquid crystal molecules are substantially aligned in one direction when no voltage is applied.
The invention further provides a spatial light modulator, comprising a plurality of the optical switching elements mentioned above, wherein the optical switching elements are arranged in a two-dimensional array or in a one-dimensional array.
The invention further provides an image display apparatus, comprising: a spatial light modulator described above; a device such that a light is made incident to the spatial light modulator; and a displaying device for projecting an image formed by the spatial light modulator to a screen.
The invention further provides an image display apparatus, comprising a spatial light modulator above; a device such that a light is made incident to the spatial light modulator; a scanning device for scanning a light emitted from the spatial light modulator in a direction perpendicular to a line direction of the optical switching elements of the spatial light modulator; and a displaying device for projecting an image formed by the spatial light modulator to a screen.
The invention further provides an optical path element, comprising: a light incident unit such that an incident light is made incident through a light transmitting element; a light reflection unit for reflecting the incident light from the light incident unit; a light emitting unit for emitting a reflection light reflected by the light reflection unit out of the light transmitting element; an index variable material filled into an optical path in the light reflection unit; and a signal input device for providing a signal to the index variable material according to information to alter an index of refraction of the index variable material. The index of refraction of the index variable material is varied to a range such that the incident light is not totally reflected at an interface between the light transmitting element and the index variable material.
The light incident unit and the light emitting unit are surfaces respectively, wherein both surfaces are not in parallel. The optical switching element is switched between a first state and a second state, wherein the first state is that the total reflection occurs at the interface between the light transmitting element and an external material surrounding the light transmitting element, and the second state is that no total reflection occurs. The optical path element further comprises a second light transmitting element such that the incident light is emitted through the second light transmitting element.
The optical path element further comprises a light transmitting plate that is optically in contact with the light incident unit of the light transmitting element and has an index of refraction substantially the same as that of the light transmitting element. The light reflection unit comprises two surfaces with a shared common edge, an angle formed between a normal line of one of the surfaces of the light reflection unit and a normal line of the surface forming the light incident unit is less than 90xc2x0xe2x88x92xcex82max, wherein the angle xcex82max is defined as a maximum of an angle formed between the normal line of the surface forming the light incident unit and the incident light that enters the index variable material. 22. The optical path element of any one of claim 16 to claim 21, wherein a plurality of reflection surfaces is formed on the reflection unit, wherein reflection surfaces correspond respectively to elements used for applying external signals to the index variable material.
The index variable material mentioned above can comprise a liquid crystal or a compound of a polymer and a liquid crystal, such that the liquid crystal is dispersed in a polymer matrix. The liquid crystal is a droplet having a grain size below one-fifth wavelength of the incident light. All liquid crystal molecules are substantially aligned in one direction when no voltage is applied.
The invention further provides a spatial light modulator, comprising a plurality of the optical path elements mentioned above, wherein the optical switching elements are arranged in a two-dimensional array or in a one-dimensional array.
The invention further provides an image display apparatus, comprising: a spatial light modulator described above; a device such that a light is made incident to the spatial light modulator; and a displaying device for projecting an image formed by the spatial light modulator to a screen.
The invention further provides an image display apparatus, comprising a spatial light modulator above; a device such that a light is made incident to the spatial light modulator; a scanning device for scanning a light emitted from spatial light modulator in a direction perpendicular to a line direction of the optical path elements of the spatial light modulator; and a displaying device for projecting an image formed by the spatial light modulator to a screen.